The present invention relates to the use of compounds and compositions as corrosion inhibitors in situations where they may come into contact with the natural environment e.g. by discharge of produced water, and to a method of inhibiting corrosion using these materials. In one preferred aspect, the present invention relates to the use of a nontoxic corrosion inhibitor in oil field acidizing operations.
In order to preserve metals, and particularly ferrous metals, in contact with corrosive liquids in gas and oil field applications, corrosion inhibitors are added to many systems, e.g. cooling systems, refinery units, pipelines, steam generators, oil production units, and oil field treating fluids. A variety of corrosion inhibitors are known. For example, GA-B-2009133 describes the use of a composition which comprises an amine-carboxylic acid such as dodecylamine propionic acid, and a nitrogen-containing compound containing an organic hydrophobic group, such as N-(3-octoxypropyl)-propylenediamine.
EP-A-256802 describes a method of inhibiting corrosion of metal surfaces in contact with a corrosive hydrocarbon-containing medium comprising contacting the metal surfaces with the reaction product of (a) tallow triamine or tallow tetramine and (b) an acrylic acid type compound, in which the ratio of the two reagents is preferably 1:1.
Although corrosion inhibitors of many types are known, the materials which have been found most effective in practice have the disadvantage of toxicity to the environment. Toxicity to the marine or freshwater environment is of particular concern. In gas and oil field applications, much work is done off-shore or on the coast. If a corrosion inhibitor enters the sea or a stretch of fresh water, on land or in lakes or streams, even at relatively low concentrations, the corrosion inhibitor can kill microorganisms, causing an imbalance in the environment. Attempts have therefore been made to identify materials which are successful corrosion inhibitors but at the same time are less toxic to the environment than known inhibitors. The applicants have found that adducts of a fatty amine and an unsaturated acid in which the product contains no primary amino groups, and only secondary or tertiary, more preferably tertiary, amine groups has a lower toxicity to the environment (referred to as ecotoxicity).